State-owned Petroleos Mexicanos said Wednesday that 29 people perished in an explosion and subsequent fire at a gas plant in the northeastern state of Tamaulipas, three more than the company reported earlier.

Pemex employees accounted for four of the dead, while the other 25 were contractors, the state oil monopoly said in a statement.

Six people injured in the accident are being treated at the Pemex regional hospital in Tamaulipas and another worker was taken to a specialized medical facility in Mexico City.

The explosion occurred around 10:45 a.m. Tuesday at the gas facility near Reynosa, a city just across the border from McAllen, Texas.

Pemex CEO Juan Jose Suarez Coppel said he asked the Mexican Attorney General's Office to launch an investigation of the accident, the company's worst since Oct. 23, 2007, when 22 workers died on an offshore oil platform in the Gulf of Mexico.

The federal AG's office, in coordination with authorities in Tamaulipas, has already assembled a team of more than 20 technical experts to carry out the probe.

Investigators are at the scene collecting evidence and talking to witnesses, the AG's office said. EFE